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Richard LawsonCentral Manchester Nuclear Medicine Centre

[email protected]

Renogram ProcessingThe Manchester Method

Radionuclides in Nephrourology, Mikulov 2010

Richard Lawson Central Manchester Nuclear Medicine Centre

The Manchester Method• Renogram processing

• Optimised background subtractionRutland method is preferred

• Renogram display• Curves normalised to administered activity

To get an idea of absolute function• Using consistent display parameters

To aid serial comparison of studies• ‘ManRen’

• Manchester Renogram processing programIncorporates these features

Optimum Background Subtraction


Renogram Curves

• Raw kidney ROI curve has three components• Tissue background, blood background & kidney activity,

• Two background components to be subtracted• Difficult to achieve with single ROI

• After correct subtraction curve should rise from origin• Because kidney activity must start from zero

Kidney ROI curve

+ Kidney

+ BloodTissue

cps

Time

Background subtracted

Kidney

cps

Time


The Rutland Method *• Two background ROIs

• Tissue backgroundSubtracted in proportion to size of ROI

• Vascular backgroundSubtraction factor calculated individually for each kidney

Using the Rutland Plot• Advantages

• Deals well with kidneys with different vascularity• Robust and reliable

• Recommended by ISCORN Consensus Report• Prigent et.al. Sem.Nucl.Med. 1999, 24:146-159

* Rutland MD Nuc.Med.Comm 1985, 6: 11-20


Background below kidney

Relative functionLeft kidney: 76%Right kidney: 24%

Right kidney under-subtracted(still some vascular background present)Relative function over-estimated

L R

Left Kidney

Right Kidney


Background above kidney


Right kidney over-subtracted(too much vascular background subtracted)Relative function under-estimated

Left Kidney

Right Kidney


Peri-renal background


Right kidney over-subtracted(too much vascular background subtracted)Relative function under-estimated

L R

Left Kidney

Right Kidney


Rutland Method


Both kidneys correct subtractionRelative function correct

L R

Left Kidney

Right Kidney

The Importance of Good Renogram Display


Serial Renograms

Question 1 Has kidney function changed since previous renogram?1=No change, 2=Got worse, 3=Got better, 4=Can’t tell

Answer: Can’t tellHalf cps could be change from 100 MBq to 50 MBq doseor change from LEHS to LEGP collimator

Left kidney

Right kidney

0

CPS

15 20minutes0 5 10

250

200

150

100

50Left kidney

Right kidney

0

CPS

15 20minutes0 5 10

500

400

300

200

100

Previous renogram Current renogram


Scale Uptake to Percent Dose

Left kidney

Right kidney4

3

2

1

0

% uptake

15 20minutes

0 5 10

5

Percent uptake normalises kidney counts to administered activityAllows for:� Different administered activities � Different collimators� Different gamma camera


More Serial Renograms

Answer: No change – still 3% at 3 minutesConfused by change of vertical scaleComputer has scaled each display to maximum in both curves

Left kidney

Right kidney4

3

2

1

0

% uptake

15 20minutes0 5 10

5

Previous renogramwith furosemide

Current renogramwithout furosemide

Question 2: Has function of left kidney changed since previous?1=No change, 2=Got worse, 3=Got better, 4=Can’t tell

Left kidney

Right kidney

3

2

1

0

% uptake

15 20minutes0 5 10

Furosemide


Standardise Vertical Scale

• Fixed maximum for vertical scale makes comparison of two studies easier• We use 15% of dose because normal MAG3 fits easily within this

• Can see at a glance that these kidneys have poor uptake compared with normal

Left kidney

Right kidney

10

5

0

% uptake

15 20minutes

0 5 10

15

‘Normal’ Renogram


Another Patient

Answer: No change – still peaks at 2½ minutesChange of horizontal scale has changed shape of peakComputer has scaled each display to duration of study

Previous renogram Current renogram

Question 3: Has emptying of left kidney changed?1=No change, 2=Got worse, 3=Got better, 4=Can’t tell

Left kidney

Right kidney10

5

0

% uptake

30 40minutes0 10 20

15

Left kidney

Right kidney10

5

0

% uptake

15 20minutes0 5 10

15


Standardise Horizontal Scale

• Use standard scales for all renograms40 min is longest of any of our renograms

• Makes serial comparison easy• Makes comparison with ‘normal’ pattern easy

10

5

0

% uptake

30 40minutes0 10 20

15

5 15 25 35

Right kidney

Left kidney

‘Normal’Renogram


ISCORN Recommendations *• ISCORN Consensus Report recommends

• Curves displayed as cps• Y axis should be scaled to highest peak count

• But changing Y axis each time is confusing• And cps give no idea of absolute function

• Because cps depends on dose and collimator• Conversion from cps to percent uptake gives a measure of absolute function• Percent uptake will correlate with renal clearance

eg GFR or ERPF• So how do we calculate percent uptake . . . . * Prigent et.al. Sem.Nucl.Med. 1999, 24:146-159


Calculating Percent Uptake

• Administered activity• Measure each patient dose in isotope calibrator• Decay factor• Calculated from time between dose measurement

and patient injection• System sensitivity

• Measured once for each camera & collimator used

% Uptake =Kidney cpsDose cps X 100 %

From renogram

X Decay factorX Sensitivity (cps/MBq)

Dose cps = Administered activity (MBq)


Sensitivity Measurement• Known activity in saline bag

• approx 2 MBq• In bowl of water

• 7.5 cm below surface• Acquire 1 min image

• with gamma camera• Draw ROI round bag

• as for kidney• Draw background ROI

• as for kidney background• Calculate net counts

• after background subtraction• Calculate sensitivity

• cps/MBq at 7.5cm depth

Gamma Camera

Plastic bowl 7.5 cm

Saline bag Water


Allowing for Kidney Depth• This standard sensitivity measurement assumes both kidneys lie at 7.5cm depth• This is adequate for most adults

• For children kidneys are not so deep• Estimate kidney depth based on child’s weight *• Increase sensitivity by 12% per cm less depth

• Can easily use any other formula for kidney depth• Or enter measured depths for each kidney

* Gordon et.al. Nuc. Med. Comm. 1987, 8: 661-670.


‘ManRen’ Program Display

Percent dose not cps

Fixed vertical scale

Functional results

Summed 5min images

Processing parameters

Regions & curves in

same colour

Rutland background method

Fixed time scale


Conclusion• In Manchester we believe that all these features are an aid to correct interpretation of the renogram• We have been using them for over 20 years• ISCORN recommendations recognise the advantage of the Rutland method for background subtraction• But contradicts the Manchester display method• We believe that display using percent uptake rather than cps gives an indication of absolute function

• Using fixed axes makes serial comparison easier• ‘ManRen’ is an in-house Aladdin program that runs on GE Xeleris computers• It incorporates all these features• Used by several hospitals in the UK

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